AC electrical machines are used in a large number of applications including, but not limited to, factory automation, wind turbines and electric drive vehicles. Typical AC electric machines include induction machines and synchronous machines. FIG. 1 is a schematic diagram illustrating a permanent magnet synchronous generator (“PMSG”) wind turbine. A PMSG is a form of a permanent magnet synchronous machine (“PMSM”). In FIG. 1, the PMSG 101 stator winding is connected to an electrical grid 103 through a frequency converter 102 (e.g., in this instance a pulse width modulated (“PWM”) converter). The frequency converter 102 can include two self-commutated PWM converters 102A and 102B, i.e., machine-side converter 102A and grid-side converter 102B, with an intermediate DC voltage link 102C. The DC voltage link 102C (e.g., a capacitor) decouples the operation of the two PWM converters, thus allowing their control and operation to be optimized. The control objectives of the machine-side converter 102A include 1) maximum energy extraction from the wind, and 2) management of PMSG energy generation in compliance with grid demands.
The performance of an AC electric machine depends on how it is controlled. Conventionally, vector control technologies have been used to control AC electric machines based on proportional-integral-derivative (“PID”) control technology. Recent studies, however, indicate that such control strategies have limitations, particularly when facing uncertainties.
Referring now to FIG. 2, a schematic diagram illustrates another type of PMSM, one used in an electric drive vehicle (“EDV”). In FIG. 2, the PMSM 201 is connected to battery 203 (e.g., a power source) through a frequency converter 202 (e.g., a PWM converter). Similar to the PMSG, the control design of PMSM is primarily model based and/or uses PID control technology, which may be inefficient, unstable and unreliable especially under variable and complex system conditions.
Therefore, what are needed are improved control systems for controlling PMSMs. In particular, systems, methods and devices are desired for controlling PMSMs under unstable and uncertain system conditions.